I am wrong?

I’m currently 10 weeks with my 3rd child. We planned this baby I was super excited and the minute I found out I was looking at baby clothes ect. Last week I found out I had an STI which I received from my husband who most likely cheated before we got married. Anyways... I am moving past it but I just feel unhappy now with this pregnancy. I just feel so stressed with the 2 kids we have and I am feeling like I want to terminate the pregnancy. I don’t know if I’m feeling this because what he did or if I truly didn’t want another child. I had a ultrasound today and I just don’t feel happy like I was with my other two. Please tell I’m not a horrible mother :(